1. Field of the Invention
The invention relates to a data carrier which includes receiver means for receiving a carrier signal modulated in respect of a signal parameter and with a given modulation intensity, and includes an integrated circuit which includes connection means which are connected to the receiver means, a demodulation stage which is connected to the connection means, is arranged to demodulate the modulated carrier signal and to output a demodulated carrier signal, and has a sensitivity adapted to the given modulation intensity used for the modulated carrier signal, and includes signal processing means which succeed the demodulation stage and are arranged to process the demodulated carrier signal.
The invention also relates to an integrated circuit for a data carrier, which circuit includes connection means for receiving a carrier signal modulated in respect of a signal parameter and with a given modulation intensity, includes a demodulation stage which is connected to the connection means, is arranged to demodulate the modulated carrier signal and to output a demodulated carrier signal, and has a sensitivity adapted to the given modulation intensity used for the modulated carrier signal, and includes signal processing means which succeed the demodulation stage and are arranged to process the demodulated carrier signal.
2. Description of the Related Art
A data carrier of the kind set forth in the first paragraph and an integrated circuit of the kind set forth in the second paragraph are known from commercially available data carrier systems which are often also referred to as transponder systems. In order to transmit data from a write/read station to a data carrier (transponder) in such a data carrier system, a carrier signal is modulated in the write/read station, that is to say in dependence on the data to be transmitted. Such a known data carrier system utilizes modulation in the form of amplitude modulation, so that the write/read station transmits an amplitude modulated carrier signal to a data carrier; this amplitude modulated carrier signal is demodulated by means of a demodulation stage which is included in the known data carrier, i.e. an amplitude demodulation stage, so that subsequent to the demodulation there is obtained a demodulated carrier signal wherefrom the data transmitted to the known data carrier can be derived.
In the known data carrier system, or in the known data carrier, a carrier signal is subjected to an ampitude modulation where the modulation intensity, i.e. the so-called modulation percentage, amounts to essentially 100%. The advantage of such amplitude modulation resides essentially in the fact that the amplitude modulation means required for this purpose can be constructed simply as an integrated circuit. How ever, such an amplitude modulation with a modulation intensity or modulation percentage of 100% has a drawback in that, when this amplitude modulation is used, the side band signals then occurring during the transmission have a comparatively high level; this often gives rise to problems in complying with country specific rules and regulations in respect of interference effects.
It is an object of the invention to avoid the described problems in a data carrier of the kind set forth in the first paragraph and in an integrated circuit of the kind set forth in the second paragraph, and to realize an improved data carrier and an improved integrated circuit in a simple way and while using only few means.
In order to achieve this object for a data carrier of the kind set forth in the first paragraph according to the invention the data carrier is arranged to receive at least one additional carrier signal which is modulated in respect of the same signal parameter but with an other, given modulation intensity, the circuit including at least one additional demodulation stage which is also connected to the connection means and has an other sensitivity which is adapted to the other, given modulation intensity used for the additional modulated carrier signal, there being provided priority means which ensure that priority is granted each time to one demodulation stage only, that a demodulated carrier signal reaches the signal processing means only from this one demodulation stage and that, in the case of simultaneous demodulation of a modulated carrier signal by means of at least two demodulation stages, priority is granted each time to the demodulation stage having the each time lowest sensitivity, and that a demodulated carrier signal reaches the signal processing means only from this one demodulation stage.
In order to achieve the above object for an integrated circuit of the kind set forth in the second paragraph according to the invention the data carrier is arranged to receive at least one additional carrier signal which is modulated in respect of the same signal parameter but with an other, given modulation intensity, the circuit including at least one additional demodulation stage which is also connected to the connection means and has an other sensitivity which is adapted to the other, given modulation intensity used for the additional modulated carrier signal, there being provided priority means which ensure that priority is granted each time to one demodulation stage only, that a demodulated carrier signal reaches the signal processing means only from this one demodulation stage and that, in the case of simultaneous demodulation of a modulated carrier signal by means of at least two demodulation stages, priority is granted each time to the modulation stage having the each time lowest sensitivity, and that a demodulated carrier signal reaches the signal processing means only from this one demodulation stage.
As a result of the steps proposed according to the invention, using means which can be comparatively simply implemented, a data carrier according to the invention, or a circuit according to the invention, can receive and demodulate modulated carrier signals having different modulation intensities without special facilities being required; the priority means simply and effectively ensure that priority is always granted to the demodulation stage which offers the qualitatively best demodulated carrier signal with each time the highest signal-to-noise ratio so that only this stage outputs a demodulated carrier signal to the appropriate signal processing means.
It has been found that it is advantageous to take the steps proposed in the claims 2 and 7, because they enable a very reliable and interference-independent implementation.
The steps proposed in the claims 3 and 8 are advantageous because the demodulation stages are then used additionally for suppressing the forwarding of demodulated carrier signals to the subsequent signal processing means.
However, the steps disclosed in the claims 4 and 9 have also been found to be advantageous, because customary demodulation stages may then be used.
The steps disclosed in the claims 5 and 10 have also been found to be very advantageous, because they ensure that interference signals which occur at the outputs of the demodulation stages which have not been granted priority cannot have a disturbing effect on the desired forwarding of the demodulated carrier signal output by the demodulation stage having been granted priority.
The above and further aspects of the invention will become apparent from the embodiments described hereinafter and will be elucidated on the basis of these embodiments.
The invention will be described in detail hereinafter with reference to two embodiments which are shown in the drawings, however, without the invention being restricted thereto.